The communications revolution of the late 20th and early 21st century has fuelled a need for better, faster, and more useful communications devices. Currently, there is a need for more efficient and more effective methods for determining the parameters of incoming wireless signals. The need is most acute in the wireless communications industry but such technology can also be applied to military uses.
One problem that has arisen in the wireless communications industry is that of multipath fading. In a wireless mobile communication system, signals propagate from the transmitter to the receiver over multiple paths resulting in multipath fading. When there is no line of sight (LOS) path available from the transmitter and an antenna is located in a dense scattering environment (e.g. indoor and urban environments), the multipath fading appears to be spatially random conforming to Rayleigh statistics. A characteristic of multipath fading is fluctuations in received signal strength as a function of spatial dimensions. This results in signal reception problems for a stationary antenna. The use of multiple antennas can alleviate the spatial fading problem to some degree by providing a means of diversity gain. Recently, attention has been paid to the detection performance of the antenna in Rayleigh fading channel. While the antenna arrays can be implemented in either the base station (BS) or the mobile station (MS), the mobile station implementation is more effective as it is typically subjected to more multipath than the BS. Unfortunately, the physical size of antenna array necessary for achieving a reasonable diversity gain is several carrier wavelengths, which is incompatible with the small form factors of typical handheld receiver devices.
A similar problem regarding the physical size of antenna arrays has been encountered in GNSS (Global Navigation Satellite System) signal reception.
In a typical GNSS propagation scenario, a signal travels from a satellite to a receiver over multiple reflective paths, referred to as multipath propagation. The effect can cause fluctuations in the received signal's amplitude, phase and apparent angle of arrival, a consequence of which is spatial and temporal multipath fading. The multipath scattering nature of the propagation medium causes the received power level to fluctuate when the receiver antenna moves as little as half the wavelength of the GNSS signal. Hence, acquiring the signal in fading channels becomes a challenging problem. Using multiple antennas that exploit the spatial dimension of indoor wireless systems has resulted in significant improvements in detectability and reliability improvements. The multiple antennas are used either in the form of antenna arrays for beamforming or in the form of antenna diversity. Recently, beamforming and interference mitigation of GNSS signals have been an active research area for military and precise positioning applications.
Unfortunately, as noted above with the mobile wireless communications system, the size and shape of antenna arrays limit the applicability of exploiting this antenna diversity approach in many portable devices such as handheld GNSS receivers.
Based on the above, there is therefore a need, both in the mobile communications industry and in the GNSS field, for solutions that would avoid the size problems of antenna arrays while providing the antenna diversity that such a system provides.
It should be noted that the above fields are populated with research into this particular problem. Some of these efforts are listed below. It should be noted that all of the references below are hereby incorporated by reference.    J. D. Parsons, The Mobile Radio Propagation Channel, John Wiley & Sons LTD, 2nd ed. 2000.    C. V. Rensburg, and B. Friedlander, Transmit Diversity for Arrays in Correlated Rayleigh Fading, IEEE Trans. Vehicular Tech., Vol. 53, No. 6, pp. 1726-1734, November 2004.    C. V. Rensburg, and B. Friedlander, The Performance of a Null-Steering Beamforming in Correlated Rayleigh Fading, IEEE Trans. Signal Processing, Vol. 52, Bo. 11, pp. 3117-3125, November 2004.    J. S. Colburn, Y. Rahmat-Samii, M. A. Jensen, and G. J. Pottie, Evaluation of Personal Communications Dual-Antenna Handset Diversity Performance, IEEE Trans. Vehicular Tech., Vol. 47, pp. 737-744, August 1998.    C. Caini, G. E. Corazza and A. Vanelli-Coralli, DS-CDMA Code Acquisition in the Presence of Correlated Fading-Part I: Theoretical Aspects, IEEE Trans. Communications, Vol. 52, No. 7, pp. 1160-1167, July 2004.    C. Caini, G. E. Corazza and A. Vanelli-Coralli, DS-CDMA Code Acquisition in the Presence of Correlated Fading-Part II: Application to Cellular Networks, IEEE Trans. Communications, Vol. 52, No. 8, pp. 1397-1407, August 2004.    S. Kim, Acquisition Performance of CDMA Systems with Multiple Antennas, IEEE Trans. Vehicular Tech., Vol. 53, No. 5, pp. 1341-1353, September 2004.    B. Friedlander and S. Scherzer, Beamforming Versus Transmit Diversity in the Downlink of a Cellular Communications Systems, IEEE Trans. Vehicular Tech., Vol. 53, No. 4, pp. 1023-1034, July 2004.    S. Stergiopoulos and H. Urban, A new passive synthetic aperture technique for towed arrays, IEEE Journal of Oceanic Eng., Vol. 17, No. 1, pp. 16-25, January 1992.    A. Broumandan, T. Lin, A. Moghaddam, D. Lu, J. Nielsen and G. Lachapelle, Direction of Arrival Estimation of GNSS Signals Based on Synthetic Antenna Array, Proceedings of ION GNSS, Fort Worth, Tex., 25-28 Sep. 2007.    S. Hyeon, Y. Yun, H. Kim and S. Choi, Phase Diversity for an Antenna-Array System with a Short Interelement Separation, IEEE Trans. Vehicular Tech., Vol. 57, No. 1, pp. 206-214, January 2008.    Y. Wang and J. R. Cruz, Performance Enhancement of CDMA Cellular Systems with Augmented Antenna Arrays, IEEE J. Select. Areas Commun., Vol. 19, pp. 1052-1060, June 2001.    O. Shin and K. B. Lee, Use of Multiple Antennas for DS/CDMA Code Acquisition, IEEE Trans. Wireless Communication, Vol. 2, No. 3, pp. 424-430, May 2003.    S. Choi and D. Shim, A Novel Adaptive Beamforming Algorithm for a Smart Antenna System in a CDMA Mobile Communication Environment', IEEE Trans. Vehicular. Tech., Vol. 49, No. 5, pp. 1793-1806, September 2000.    H. L. V. Trees, Detection, Estimation, and Modulation Theory, part I, John Wiley & Sons, Inc., New York, 2001.    H. L. V. Trees, Optimum Array Processing, part IV, Detection, Estimation, and Modulation Theory, John Wiley & Sons, Inc., New York, 2002.    S. M. Kay, Fundamentals of Statistical Signal Processing Detection Theory, Prentice-Hall, Inc, 1998.    J. Liberti and T. S. Rappaport, Smart Antennas for Wireless Communications: IS-95 and Third Generation CDMA Applications, Prentice Hall, 1999.    E. D. Kaplan, and C. Hegarty, Understanding GPS Principles and Applications, 2nd ed., Artech House 2006.    O. Shin, and K. B. Lee, “Use of Multiple Antennas for DS/CDMA Code Acquisition,” IEEE Trans. Wireless Communication, Vol. 2, No. 3, pp. 424-430, May 2003.    S. Hyeon, Y. Yun, H. Kim, and S. Choi, “Phase Diversity for an Antenna-Array System with a Short Interelement Separation,” IEEE Trans. Vehicular Tech., Vol. 57, No. 1, pp. 206-214, January 2008.    G. Seco-Granados, A. Fernandez-Rubio and C. Fernandez-Prades, “ML Estimator and Hybrid Beamforming for Multipath and Interference Mitigation in GNSS Receivers,” IEEE Trans. Signal Processing, Vol. 53, No. 3 pp. 1194-1208 March 2005.    A. Brown and N. Gerein, “Test Results of a Digital Beamforming GPS Receiver in a Jamming Environment,” Proceedings of ION GPS, Salt Lake City, September, 2001.    Z. Fu, A. Hornbostel, and A. Konovaltsev “Suppression of Multipath and Jamming Signals by Digital Beamforming for GPS/Galileo Applicaions,” GPS Solutions, pp. 257-264, 2003.    Y. L. Jong, and M. Herben, “High-resolution Angle of Arrival Measurement of the Mobile Radio Channel,” IEEE Trans. Antennas Propagat., Vol. 47, No. 11, pp. 1677-1687, November 1999    S. Khalesehosseini, and J. Nielsen, “Generalized CRLB for DA and NDA Synchronization of UWB Signals with Clock Offset,” Proceedings of ICC 2007, Glasgow, Scotland, pp. 4305-4310.    Y. Chen, and N. C. Beaulieu “CRLBs for NDA ML Estimation of UWB Channels,” IEEE Communication Letters, vol. 9. no. 8, pp. 709-711, August 2005.    T. S. Rappaport, Wireless Communications: Principles and Practice, Prentice Hall PTR, 2nd Edition, 2002.    B. Zheng, G. Lachapelle “GPS Software Receiver Enhancements for Indoor Use,” ION GNSS, 18th International Technical Meeting of the Satellite Division, Long Beach, Calif., 2005.    T. L. Fulghum, K. J. Molnar, and A. Duel-Hallen, “The Jakes Fading Model for Antenna Arrays Incorporating Azimuth Spread,” IEEE Trans. Vehicular Tech., Vol. 51, No. 5, pp. 968-977, September 2002.    W. C. Jakes, Microwave Mobile Communications. 2nd ed. Piscataway, N.J.: Wiley-IEEE Press 1974.